The first 2 Paraffin tests were Spectrographic analysis & Neutron Activation analysis. The first is a basic test considered reliable for all criminal investigations. The second test is even more reliable since it's capable of identifying the presence of substances in quantities too small to be captured by spectrographic analysis. That test required the use of a nuclear reactor, thus was carried out for the FBI at a reactor owned by the Atomic Energy Commission. The results of that test were hidden until two decades after the assassination, and were only made public as the result of a court case, (Weisberg v. ERDA and the Department of Justice, Civil Action 75–226). Those results are in the Harold Weisberg archive.
The results of one of the NAA tests was mentioned in the Warren Report, indicating the casts, which had been washed, had become contaminated:
"The paraffin casts of Oswald's hands and right cheek were also
examined by neutron-activation analyses at the Oak Ridge National
Laboratory. Barium and antimony were found to be present on both
surfaces of all the casts and also in residues from the rifle cartridge
cases and the revolver cartridge cases."
The absence of residue on Oswald's face meant he had not fired a rifle that day.
Crime Lab Sgt. W.E. Barnes was ordered by Fritz to conduct a paraffin test on Oswald's right cheek, the first time Barnes ever had such an order regarding a suspect's face. Barnes knows beforehand it will most likely prove negative.
FBI expert Cortlandt Cunningham testified:
"I personally wouldn’t expect to find any residues on a person’s right
cheek after firing a rifle due to the fact that . . . the cartridge itself is
sealed into the chamber by the bolt being closed behind it, and upon
firing the case, the cartridge case expands into the chamber filling it
up and sealing it off from the gases, so none will come back in your
face, and so by its very nature, I would not expect to find residue on
the right cheek of a shooter."
It would do Cunningham no good to lie about this, knowing other experts would vet his testimony. Cunningham acknowledged the tests weren't proof of a weapon being used:
"The theory of the test is that it is a test for gunpowder residues. Now,
that is the theory, and it is fallacious, inasmuch as the reagents used
in these two tests are not specific for gunpowder residues. Now, it is
true that the nitrates and nitrites in gunpowder residues will react
positively with diphenylamine and diphenylbenzidine, but they are
not specific. They will react--these two reagents will react with most
oxidizing agents."
Your claim the "the FBI failed to mention was that barium and antimony are also found in several common substances" would appear to be wrong, as Cunningham went on to testify:
"Urine, tobacco, cosmetics, pharmaceuticals, soil, fertilizer--I have a list
here of the different families or classes of compounds that will react.
In addition to nitrates and nitrites, substances such as dichromates,
permanganates, hypochlorites, periodates, some oxides, such as
selenium dioxide and so forth. Also, ferric chloride and chromates and
chlorates. The list of oxidizing agents is so large that will react--that
you cannot specifically say it was a gunpowder residue."
The Warren Report stated:
"A positive reaction is, therefore, valueless in determining whether a
suspect has recently fired a weapon. Conversely, a person who has
recently fired a weapon may not show a positive reaction to the
paraffin test, particularly if the weapon was a rifle."
The other reason is because it not only proves Oswald innocence, but add it to all the other things the FBI & Police stated & used to show guilt, it reveals just how far these men of law went to frame an innocent man, American citizen and United States Marine.
I don't think flag-waving and an appeal to patriotism is appropriate here. If in the business of framing young Oswald, why not have Barnes concoct a "positive" cheek test and have Cunningham testify that proves Oswald fired a rifle?
What is clearly dishonest is the claim that a negative result for the cheek means Oswald was innocent.
The third Paraffin test was done on 7 marksmen who fired similar rifles to that of the 6th floor one. And all 7 showed substantial traces of residue on both their hands and cheeks.
Again, from the Warren Report:
"In a third experiment, performed after the assassination, an agent of the
FBI, using the C2766 rifle, fired three rounds of Western 6.5-millimeter
Mannlicher-Carcano ammunition in rapid succession. A paraffin test
was then performed on both of his hands and his right cheek. Both of
his hands and his cheek tested negative."
Cunningham said the agent's face and hands, and the parts of the rifle he might come into contact with, were washed with a non-oxidizing cleanser before each test-firing. Cunningham was the only one to touch the clip, and so forth, before the other agent fired the rifle. It would appear the GSR (gunshot residue) was escaping from the barrel.
Do we know the precautions taken by the "7 marksmen"?